1. Technical Field
This disclosure relates generally to an elevator and, more particularly, to a system and method for actively damping vertical oscillations of an elevator car.
2. Background Information
An elevator typically includes a plurality of belts or ropes that move an elevator car vertically within a hoistway between a plurality of landings. When the elevator car is stopped at a respective one of the landings, changes in magnitude of a load within the car can cause changes in vertical position of the car relative to the landing. The elevator car can move vertically down relative to the landing, for example, when one or more passengers and/or cargo move from the landing into the car. In another example, the elevator car can move vertically up relative to the landing when one or more passengers and/or cargo move from the car onto the landing. Such changes in the vertical position of the elevator car can be caused by soft hitch springs and/or stretching and/or contracting of the belts or ropes, particularly where the elevator has a relatively large travel height and/or a relatively small number of belts or ropes. Under certain conditions, the stretching and/or contracting of the ropes or belts and/or hitch springs can create disruptive oscillations in the vertical position of the elevator car; e.g., an up and down car motion.